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The present invention pertains to a method and apparatus for image enhancement, including smoothing and thinning degraded images such as camera images, scanned images, facsimile-transmitted images and images containing letters, numbers, symbols, characters and the like. More particularly, the invention is concerned with a method for processing image data so as to enhance the quality of the image.
Text or pictorial images today are often replicated or transmitted by a variety of techniques, such as photocopying, facsimile transmission, and scanning images into a memory device. Due to a variety of factors, the process of replication or transmission often tends to degrade the resulting image. Degraded images are characterized by noise spots, indistinct or shifted edges, blended or otherwise connected characters and distorted shapes. A reproduced or transmitted image that is degraded in quality may be unusable in certain applications. For example, if the reproduced or transmitted image is to be used in conjunction with character recognition apparatus, the noise spots, indistinct edges, connected characters, etc. may preclude accurate or successful recognition of characters in the image. Also, if the degraded image is printed or otherwise rendered visible, the image may be more difficult to read and in general, less visually distinct.
FIG. 6 is an example of a degraded image of the word "This." As seen in FIG. 6, a noise spot 1 clutters the image making analysis difficult. Additionally, the letters "T" and "h" are connected at 2, while the letter "h" is distorted at 3 by a break in the letter.
To improve image quality, in the case of pixel image data stored in a computer memory, it has been proposed to improve the stored image data by applying a low pass filter to it. Typically, a Gaussian filter is applied to smooth the data. Such filters purport to remove noise spots, but do so only at the expense of further blurring and/or connecting of the image and further degradation in edge sharpness.